1. Field of the Invention
The present invention relates to a portable overhead projector.
2. Description of the Prior Art
An overhead projector generally has a structure in which an image projection sheet on which an image for projection is formed is placed on a stage, the image on the image projection sheet is enlargedly projected on a screen through a projection lens by the light emanating from a light source illuminating the image projection sheet. The image projection sheet used in the overhead projector is a transparent sheet on which an image for projection is formed. The image projection sheet having an A4 size in JIS (the Japanese Industrial Standards) is generally used, in order to print out an information such as a document, an image or the like which were formed by using a personal computer, a word processor or the like, by a printer conveniently.
In order to strongly assist, for example, sales by a salesman, a good portability is required for such an overhead projector. In response to this requirement, although various types of overhead projectors have been developed and produced, there is a problem of further miniaturization being difficult because these overhead projectors have a structure in which image projection sheets having a size up to A4 can be used, so that it is impossible to make the stage smaller than the image projection sheets having an A4 size. Therefore, in the present condition, it is hardly for user, e.g., salesmen or the like, to conveniently carry such an overhead projector in their bags or the like.
In order to solve the problems in the present condition, the present inventors have aimed at the size of the image projection sheets and have made it smaller, and thus the present inventors have studied miniaturization, making light weight, and portability, of the whole device of the overhead projector. Accordingly, it has been found that there are following various problems. For example, if the image projection sheets are simply formed in a small size similar to that of a pocket notebook, because the sheets cannot be transferred by a feed roller of a printer, a copying machine or the like, it is not possible to print out an information such as a document, an image or the like which were formed by using a personal computer, a word processor or the like, by a printer conveniently. Therefore, a specific device, for example, of a photographic system or the like, is required. If the smaller image projection sheet can be used, it is possible to make the whole device small-sized by making the stage small. However, even if a small-sized overhead projector can be obtained, it is not necessarily possible to obtain one which has a good portability for salesmen to conveniently carry it in their bags. Even if the device has a good portability, it is impossible to obtain a clear good projection image when the optical path length from the light source to the projection lens cannot be ensured.